!7

import javax.swing.tree.*;

p-substance {
  DefaultMutableTreeNode rootNode = new("root");
  rootNode.add(new DefaultMutableTreeNode("dummy"));
  final JTree tree = new JTree(rootNode);
  tree.setShowsRootHandles(true);
  tree.collapseRow(0);
  
  tree.addTreeWillExpandListener(new TreeWillExpandListener {
    public void treeWillCollapse(TreeExpansionEvent e) {}
    public void treeWillExpand(TreeExpansionEvent e) throws ExpandVetoException {
      DefaultMutableTreeNode node = cast e.getPath().getLastPathComponent();
      print("treeWillExpand, node=" + node.getUserObject());
      node.removeAllChildren();
      node.add(new DefaultMutableTreeNode(str(now())));
      ((DefaultTreeModel) tree.getModel()).nodeStructureChanged(node);
    }
  });
  
  showFrame(jscroll(tree));
}

Began life as a copy of #1008646